Evaluating the mechanical performance of bio-based concrete: The role of aggregate type and orientation in compression cyclic loading

This study evaluates the effect of the physical aspects of four bio-aggregates (Hemp, bamboo, rapeseed, and reed) on the mechanical properties of bio-based concrete under cyclic compression loading. The bio-based specimens are assessed with respect to two distinct orientations of bio-aggregates: Perpendicular to compaction direction, and parallel to compaction direction. The digital image correlation (DIC) method permits to monitor strain and displacement fields throughout 19 loading–unloading cycles. Beyond conventional mechanical characterization, DIC data were processed to quantify crack density, crack length, and crack opening displacement (COD) as indicators of fatigue damage evolution. Hemp concrete exhibited the highest compressive strength and modulus, while bamboo concrete showed the weakest performance despite its higher density. In perpendicular orientation, specimens demonstrated cyclic hardening up to 4.5 % strain before entering a damage phase, whereas parallel-oriented specimens began degrading around 1.8 % strain. The useable strength of parallel-oriented specimens denotes the particle/binder affinity rather than the actual material's strength. The deformation charts given by the digital image correlation show that specimens tested under perpendicular orientation of bio-aggregates exhibit two horizontal lines of stress concentration whereas specimens tested under parallel orientation show the propagation of a vertical concentration lines. The failure mode of the perpendicular-oriented specimens is characterized by gradual crushing of bio-aggregates whereas the parallel-oriented specimens fail due to buckling that splits the specimen into two different parts on either side of the vertical concentration lines. Crack analysis revealed that hemp, reed, and rapeseed concretes developed limited and slowly propagating cracks (average rate 0.18–0.23 mm/cycle), with maximum crack lengths below 5 mm and narrow CODs (less than 2 mm). In contrast, bamboo concrete displayed rapid crack propagation (dL/dN around 3.66 mm/cycle), high crack density (32), and wide openings (higher than 4 mm), reflecting weak interfacial bonding. Hence, hemp shives oriented perpendicularly provides the ideal optimized configuration of bio-based concretes assessed in this study. • Hemp concrete showed the best mechanical and fatigue performance among bio-based mixes. • Perpendicular-oriented rigidify up to 4.5 % of strain, while parallel-oriented specimens are limited at 2 % of strain. • Perpendicular orientation enhanced strength and reduced crack growth under cyclic loading. • Bamboo concrete exhibited poor interfacial bonding, leading to rapid crack propagation. • DIC analysis revealed orientation-dependent crack patterns and fatigue damage evolution.